1. Field of the Invention
The invention relates to a pouring spout for molten metal, such as steel, which is operative to extend into an ingot mold and through which a charge of molten steel is poured into the ingot mold.
2. Description of the Prior Art
It is known in the prior art to provide a refractory immersion pouring spout as disclosed in German Utility Model DE-GM No. 81 00 896, which corresponds to U.S. Pat. No. 4,423,833, including an upper head portion adapted to be set in an intermediate holder and a pouring tube portion extending out of and below that holder into an ingot mold. An outer protective jacket extends over the height of the pouring tube which is immersed in the molten metal bath within the ingot mold. Consequently, the jacket can only protect the outside surface of the immersion pouring tube against chemical and erosive attacks by the molten steel or by the slag in the region of the top surface of the molten metal bath. The jacket does not reduce the erosion which takes place within the interior of the delivery pouring tube. It has been found, with an immersion pouring spout of this type, that the practical service life of the pouring tube is limited by the internal erosion which occurs above the surface of the molten metal bath.
German Utility Model DE-GM No. 70 05 373 discloses an immersion molten metal pouring spout having an external jacket that extends over most of the height of the pouring tube and which jacket is not cemented to the pouring spout but is connected to it by mechanical means that prevents the jacket from extending over the entire length of the pouring tube. This sheath jacket comprises an exothermic material. The molten steel flowing out of the bottom opening in the immersion pouring spout ignites the exothermic material such that the immersion pouring spout is heated. The molten steel, therefore, does not solidify during the initiation of the pouring of a billet into the ingot mold. In the process, the jacket is consumed and must be renewed before each charge of metal into the ingot mold such that multiple charge service lives cannot be attained. After the jacket has been burned-out, the residual material provides a certain thermal insulation for the immersion pouring spout which is highest for a casting process.